Excavators, such as the one illustrated in U.S. Pat. No. 6,865,464, can be used in a wide variety of applications: in the construction industry to prepare building sites, in mining to load ore-laden material into trucks or onto conveyors, in road building to make cuts through hillsides for new road beds, in pipe laying and utility work to dig trenches. In all of these operations, excavators employ buckets to penetrate into material in the ground or in a pile, to scoop the material, and then to dump it. The bucket is the implement at the center of performing these tasks.
Excavator buckets are subjected to extreme loads and wear. An excavator bucket on a large excavator could be used to penetrate into extremely hard and dense material such as loosely shot or fractured granite. For this kind of duty, an excavator bucket requires high performance steels and a specialized construction to withstand both the high shock loads, and the extreme abrasive wear. Besides withstanding these maximum load cases and the abrasive environment, an excavator bucket must also be strong enough to endure many thousands, or in some cases, millions of cycles. (A cycle is each repetition of penetrating into the material, scooping, and dumping.) So an excavator bucket also requires resistance to fatigue wear and failure.
If an excavator bucket fails, replacement of the bucket can amount to a great expense in parts and labor. In addition, replacing a bucket will cause the excavator to sit idle and its productivity to decline, resulting in further costs. Besides idling the excavator, a bucket failure can also idle other machines in an integrated operation, such as haul trucks and crushers, further increasing the losses. Thus, a reliable excavator bucket that lasts through many cycles without breaking can be an important requirement for owners of excavator machines.
An excavator bucket can be expensive and difficult to manufacture because of its size and weight and other factors. Excavator buckets are typically constructed as weldments of more than a dozen pieces of plate steel. A bucket for a large, 60 metric ton excavator, for example, can be about 2 meters tall and 2 meters wide, weighing about 5 metric tons. Manipulating these large and heavy pieces of plate steel to align them to one another, and then correctly performing the welds can be a difficult and expensive task. A bucket design which requires a large number of pieces and multiple welds can add to the costs.
Thus, there are many demands affecting the design of an excavator bucket. The design must result in a bucket which exhibits the appropriate performance characteristics of resistance to high loads, abrasion, and fatigue, and which can also be manufactured in an economical manner. To produce a competitive bucket design, a designer must identify design features and techniques to satisfy and balance all of these demands.